1. Field of the Invention
The present invention relates to an electronic circuit device and, more particularly, to an electronic circuit device suitably used for a memory device using a semiconductor.
2. Related Background Art
The importance of memories to the current OA equipment and the like is increasing steadily. Of the memories, semiconductor memories have been variously studied and developed because of their advantages in terms of speed, power consumption, size, and the like. However, they are still inferior to other types of memories, e.g., magnetic disks, optical disks, magnetooptical disks, and CD-ROMs in many points such as capacity and cost. Therefore, semiconductor memories have limited applications at present. Although semiconductor memories include various types of memories such as SRAMs, EPROMs, EEPROMs, mask ROMs, and fuse ROMs, they can be roughly classified into two types of memories, i.e., RAMs and ROMs. They can also be classified into nonvolatile memories and volatile memories. Of these memories, large-capacity, low-cost, nonvolatile memories are expected to be promising. Nonvolatile characteristics that information is retained in the absence of power are indispensable for the future development of handy type devices. Needless to say, there are unceasing demands for an increase in capacity and a reduction in cost as well as a reduction in size. Nonvolatile memories are used in various fields at present, e.g., the fields of font storage in wordprocessors, LBPs, and the like, automatic control for musical instruments and games, and the like. That is, it is too numerous to mention all the fields. In addition, nonvolatile memories are expected to have wider applications in accordance with the trend toward multimedia. Nonvolatile memories include EPROMs, EEPROMs, RAMs called flash memories, which have recently been developed, ROMs such as mask ROMs which are programmed in the manufacturing process but cannot be programmed afterward, and OTROMs (one time ROMs which are EPROMs having no ultraviolet light erasing windows) which allow programming only once. They are selectively used in accordance with application purposes. Note that a RAM, which is programmable, may be more preferable than a memory such as a mask ROM, which allows no selection of programming by the user, depending on an application purpose.
Especially, flash memories have recently attracted a great deal of attention because they are capable of electrically writing and erasing data and expected to surpass DRAMs in capacity in the future.
The following problems, however, are posed in the above flash memories:
(1) Since a write operation is performed by injecting hot electrons into the floating gate or charges into an FN tunnel current, the threshold value in the write mode varies for each cell, resulting in an unstable operation. PA1 (2) Since the amount of charges written is small, a great variation in threshold value is caused by even a very small leakage current, and a change over time occurs. That is, the reliability is poor. PA1 (3) Since the voltage for a write/erase operation and the like is as high as 12 V, sufficient miniaturization of elements cannot be realized in the future. PA1 characterized in that one of the first and second conductors consists of a metal or metal compound, and PA1 the insulator consists of an oxide or nitride of the metal or metal compound. In this case, the metal includes an alloy, an intermetallic compound, and the like as well as a simple metal. PA1 characterized in that a negative potential is applied to one of the first and second conductors, which has a larger stepped portion, and the conductor having the larger stepped portion consists of a material having high migration resistance. PA1 characterized in that the first and second conductors are formed into a matrix and arranged on a substrate on which a circuit for driving the matrix is formed, and are connected to an upper conductor constituting the matrix within a plane of the matrix. PA1 characterized in that at least a planar film is formed between the first and second conductors.